Conventionally, construction equipment, which has a working machine such as a hydraulic shovel driven by a hydraulic cylinder, is provided with a mechanical cushion to ease a shock at a stroke end of a cylinder, the shock being caused when an operator operates a lever. If the lever is fully moved, hitting the stroke end, a conventional mechanical cushion cannot completely absorb the inertial force of the working machine, and a big noise is produced at the time of the collision, causing the vehicle body to shake. In addition, a cushion chamber is subjected to a high back pressure, adversely affecting the durability of the cylinder and also leading to higher structural cost. To solve these problems;
(1) there is a method available, wherein a cylinder stroke position is detected so that, when a dangerous zone set near the end of the stroke path is reached, the engine RPM or the angle of a swash plate is decreased to reduce the discharge quantity of a pump, thereby decreasing the speed of the cylinder, and PA1 (2) there is another method available, wherein a cylinder control valve is set back to the neutral to stop the cylinder (refer to the Japanese Published Unexamined Patent Application No. 2-57703).
They have, however, disadvantages described below:
(1) The method, wherein the engine RPM or the discharging quantity of the pump is reduced, prevents satisfactory composite operation because an engine pump is not provided on each shaft of the working machine, and therefore, each time one shaft reaches a stroke end, the working speed of other shafts unavoidably decreases. There is another disadvantage in that the engine or the pump is required to exhibit extremely high responsiveness.
(2) The method, wherein the cylinder control valve is set back to the neutral, is disadvantageous in that, when the cylinder length reaches the dangerous zone, a controller issues a signal for setting the valve back to the neutral independently of the lever operation performed by an operator, thus carrying out automatic deceleration irrespectively of operator's intent.
In general, when operating a shaft with high inertia at a full lever stroke, the dangerous zone must be secured with a certain level of ampleness in order to stop the shaft without causing a shock at a stroke end. Such conventional methods, however, make it difficult for the operator to stop the cylinder in a desired position within the dangerous zone, thus narrowing the zone for operating the working machine, wherein the operator can operate it.